Certain techniques for manufacturing semiconductor wafers involve producing a layer of a first crystalline material on a substrate of a second crystalline material that has a different nominal lattice parameter. The crystalline structure of the second material is sometimes desired to be relaxed. A known technique provides a buffer layer between the substrate and the produced layer of different nominal lattice parameter.
A typical buffer layer is a transition layer that matches the lattice parameter of the produced layer with that of the substrate. Such a buffer layer may have a composition that gradually varies along its depth by providing the buffer layer with a gradually varying composition. Buffer layers are also known with complex configurations, such as with a compositional variation or discontinuous step changes in composition. The formation of the variable composition in the buffer layer takes considerable time and expense and requires care to implement. Also, to minimize the density of crystallographic defects in the buffer layer, the thickness of a buffer layer is usually large, typically between one and several microns.
Another technique known relaxes elastic strains in a formed layer. Such a technique is disclosed in an article by B. Höllander et al. entitled, “Strain relaxation of pseudomorphic Si1-xGex/Si(100) heterostructures after hydrogen or helium ion implantation for virtual substrate fabrication” (in Nuclear and Instruments and Methods in Physics Research B 175-177 (2001) 357-367). The described process relates to the relaxation of a strained SiGe layer in compression, with this layer being formed on an Si substrate.
In this technique, hydrogen or helium ions are implanted through the surface of the strained layer into the Si substrate to a defined depth. A crystalline perturbation is created by the ion implantation and located in a thickness of the Si substrate lying between the implantation region and the SiGe layer, and this perturbation allows the SiGe layer to relax when subjected to a heat treatment.
A simple process is thus needed to readily relax a strained layer, which can be used in the production of crystalline wafers.